1. Field of the Invention
The present invention relates to a differential apparatus, and more specifically to a differential apparatus provided with a frictional differential limiting function suitable for use in an automotive vehicle.
2. Description of the Prior Art
An example of prior art differential apparatus related to the present invention is disclosed in U.S. Pat. No. 5,244,440, for instance. In this prior art differential apparatus, an engine drive power is first transmitted to a differential casing of the differential apparatus, and then distributed to both rear right and left wheels via two pairs of helical pinion gears in mesh with a pair of helical side gears, respectively. Further, the four helical pinion gears are accommodated in gear accommodating holes formed in the differential casing.
In the above-mentioned two pairs of the helical pinion gears, each helical pinion gear is composed of a first gear portion of narrow face width and a second gear portion of wide face width, and both the first and second gear portions are formed Integral with each other. In a pair of the two helical pinion gears, the first narrow face-width gear portion of the first helical pinion gear is in mesh with the second wide face-width gear portion of the second helical pinion gear. Further, the second wide face-width gear portion of the first helical gear is in mesh with one of the helical side gear, and the second wide face-width gear portion of the second helical pinion gear is in mesh with the other of the helical side gear.
When the engine drive power is being transmitted, since the helical pinion gears are urged against the wall surfaces of the accommodating holes formed in the casing, respectively due to reaction force generated by gearing among the helical pinion gears and the helical side gears, and in addition since a thrust force is generated in each of the helical pinion gears by gearing among the these helical pinion gears and the side gears, a frictional force is generated between the outer gear surfaces of each of the helical pinion gears and each of the wall surfaces of the differential casing, so that it is possible to limit the differential motion of the differential apparatus on the basis of these generated frictional forces.
Here, the differential gear limiting force generated between the helical pinion gears and the wall surfaces of the differential casing changes largely in dependence upon the helix angles of the gear teeth of the two geared helical pinion gears (described later in further detail with reference to the attached drawings). In other words, it is possible to control the differential limiting force of the differential apparatus by changing the relationship with respect to the helix gear tooth angle between the two geared helical pinion gears.
In the prior art differential apparatus, however, since the first or second helical pinion gear composed of the first and second pinion gears is formed integral with each other respectively, when the differential limiting forces of various degree in frontward and rearward travel directions are required, a number of the helical pinion gears of various helix gear tooth angles must be prepared, with the result that there exists a problem in that the kinds of parts increases and thereby the cost thereof is high. In addition, there exists another problem in that it is rather difficult to assemble a plurality (e.g., four) of helical pinion gears formed integral with both the narrow and wide face-width gear portions in the differential casing simultaneously.